1. Field of the Invention
The present invention relates to wireless communications and, more particularly, to a method and system for using a measure of spectral interference to determine whether to output signals to a wireless link.
2. Description of Related Art
In a wireless network, a wireless terminal such as a cellular telephone or a computer with wireless modem is communicatively coupled to a radio access network. The radio access network enables the wireless terminal to communicate with a remote device, e.g., a telephone or another computer.
The radio access network has a base station. The base station consists of a base transceiver station (BTS) and a base station controller (BSC). The base station is communicatively coupled to a mobile switching center (MSC) and a packet data serving node (PSDN). The MSC and the PDSN provide connectivity to a public switched telephone network (PSTN) and Internet, respectively. As a result, the wireless terminal can communicate with the remote device.
The base station exchanges signals with the wireless terminal by way of an air interface. The base station receives signals from the MSC or the PDSN and transmits the signals to the wireless terminal over the air interface. Additionally, the base station receives signals from the wireless terminal over the air interface and outputs the signals to the MSC or the PDSN. One or more wireless links communicatively couple the BTS, the BSC, and the MSC or the BTS, BSC, and the PDSN. And one or more wired links communicatively couple the MSC to the PSTN and the PDSN to the Internet.
In an ideal environment, the wireless links reliably carry the signals between the base station and the MSC and the base station and the PDSN. In reality, however, other signals interfere with the signals carried by the wireless links. The other signals are from licensed and unlicensed devices that transmit within a range of frequencies defined for the wireless links. Additionally, the other signals are from multi-path reflections of the signals carried by the wireless links. The interference from the other signals is commonly referred to as spectral interference. Spectral interference introduces errors into the signals carried by the wireless links, thus reducing a reliability of the wireless links.
The spectral interference is characterized by a bit error rate (BER) or a signal to noise (S/N) ratio. The BER is a measure of a number of bits that are received through a wireless link in error during a period of time. On the other hand, the S/N is a measure of signal strength of signals received over the wireless link as compared to noise over the wireless link. The signals received over the wireless link may be those signals carried by the wireless link. And the noise may be background noise, licensed signals, and unlicensed signals that exist within the range of frequencies defined for the wireless link.
To minimize the spectral interference for the wireless link, a service provider typically performs a truck roll-out. The truck roll out involves the service provider going out to end points of the wireless link and, using a spectral analyzer, making one or more spectral interference measurements. The service provider then uses the spectral interference measurements to configure the wireless link so that the spectral interference for the wireless link is at a predefined level.
The service provider can configure the wireless link in many ways so that the spectral interference is at the predefined level. For instance, if an endpoint of the wireless link transmits signals over a first range of frequencies and receives signals over a second range of frequencies, then the service provider can reduce the spectral interference by reversing the range of frequencies at which the signals are transmitted and received. For example, the wireless link may be reconfigured to receive signals over the first range of frequencies and transmit signals over the second range of frequencies. As a result, the spectral interference in the second range of frequencies no longer poses a problem because the signals are now received over the first range of frequencies. Additionally or alternatively, the service provider may increase power of the signals that are transmitted so as to overcome the spectral interference. Still additionally or alternatively, the service provider may increase strength of a received signal by deploying a high-gain antenna. The high-gain antenna allows for increased strength of the received signal and transmission of more a focused signal, thereby overcoming the spectral interference.